1. Field of the Invention
The present invention relates to a toner for electrostatic image development used for the development of a latent image formed in electrophotography, electrostatic recording method, electrostatic printing method or the like.
2. Discussion of the Related Art
When toners are fixed onto paper or the like, a heat roller fixing method is generally used from the viewpoint of thermal efficiency, but an offset phenomenon is likely to be caused. In addition, lowering a lowest fixing temperature and broadening a fixable temperature range are necessitated for energy conservation, and there is earnestly desired the development of toners which are more excellent in the durability, i.e., toners with no contamination of a fixing roller after long-term use.
Conventionally, in order to improve the offset resistance, there have been tried measures against hardware such as a method comprising coating a surface of a fixing roller with a silicone rubber or a fluororesin and applying thereto a releasing agent such as a silicone oil, and those against software such as toner materials such as a method of blending polyesters having different softening points (Japanese Patent Laid-Open No. Hei 4-362956 (corresponding to U.S. Pat. No. 5,234,787)); and a method of addition of a polyvalent metal salt (Japanese Patent Laid-Open No. Sho 59-29256). However, a larger apparatus is required in the measures against external, and a sufficient fixable temperature range cannot be obtained in the measures against internal. In addition, a sufficient durability cannot be obtained in either case, so that a further improvement is desired in light of the current demand for miniaturization and higher speed.
An object of the present invention is to provide a toner for electrostatic image development which has a wide fixable temperature range and a low lowest fixing temperature, and which is excellent in the durability.
These and other objects of the present invention will be apparent from the following description.
As a result of intensive studies, the present inventors have found that the above problems can be solved by using particular polyesters and various particular composite oxides, and perfected the present invention.
The present invention relates to a toner for electrostatic image development comprising:
a high-softening point polyester having a softening point of 120xc2x0 C. or more and 170xc2x0 C. or less;
a low-softening point polyester having a softening point of 80xc2x0 C. or more and less than 120xc2x0 C.; and
a composite oxide of two or more metals, wherein the composite oxide has a BET specific surface area of 7 m2/g or more.